Radiotherapy and Nuclear Pharmacy

Question 1

what is a nuclide?

Answer 1

species of an atom with a specific number of protons and neutrons in its nucleus

Question 2

what is radioactivity?

Answer 2

Spontaneous transformation of an unstable nucleus to a more stable nucleus with release of ionising radiation…

Question 3

what is ionizing radiation?

Answer 3

radiation with enough energy that when it interacts with an atom it can remove bound electrons

Question 4

what are the different radiation types?

Answer 4

Alpha – Positively charged He nuclei (2 protons + 2 neutrons)

Beta – Electrons

X-rays – EM radiation

Gamma – EM radiation

Question 5

when is X-rays emitted?

Answer 5

X-rays are emitted when a target of heavy metal atoms is bombarded by energetic electrons

Question 6

what is the charge of Alpha - a
mass of particles
penetrating power?
most damaging source?

Answer 6

positive

heavy particles

very low penetrating power

Most damaging source: Internal

Question 7

what is the charge of Beta - B
mass of particles
penetrating power?
most damaging source?

Answer 7

negative

light particles

low penetrating power

most damaging source: internal

Question 8

what is the charge of X-ray
mass of particles
penetrating power?
most damaging source?

Answer 8

neutral

no mass

very high penetrating power

most damaging source: external

Question 9

what is the charge of Gamma- y
mass of particles
penetrating power?
most damaging source?

Answer 9

neutral

no mass

very high penetrating power.

most damaging source - External

Question 10

what is the harmful effects of radiation?

Answer 10

harmful effects
- Depend on the energy and penetration power of the radiation as well as the time of exposure
- Include nausea, skin burns, loss of hair, sterility, cancer and even death
- Causes mutation in DNA

Question 11

why do we use radiation
useful applications?

Answer 11

-Treatment of cancers
- Sterilising medical instruments and biomaterials
- Finding leaks
- Dating archaeological remains
- Generating electricity

Question 12

what radiation is more internally damaging?

Answer 12

alpha-a
beta- b

Question 13

what radiation is externally damaging

Answer 13

x-ray
gamma- y

Question 14

what is half life?
radiopharmacuetical can be classified into long and short half life - what is it?

Answer 14

Half-life is the time it takes for the activity, or the amount of a radioactive isotope, to fall by half. The shorter the half life, the faster the isotope decays and the more unstable it is.

Radiopharmaceuticals can be classified into long and short half-life products.
Long half-life > 12 hrs
Short half-life < 12 hrs

Question 15

what is the activity of a radioactive source?

Answer 15

The activity of a radioactive source is the number of nuclear transformations per unit time

1 Becquerel (Bq) is one disintegration per second (SI unit)
1 megabecquerel (1 MBq) = 106 Bq
1 kilobecquerel (1 kBq) = 103 Bq

1 curie (Ci) – 3.7×1010 disintegrations per second (dps)
1 millicurie (1 mCi) = 10-3 curie
1 microcurie (1 Ci) = 10-6 curie
1 nanocurie (1 nCi) = 10-9 curie

disintegration is an example of nuclear transformation

Question 16

what is an absorbed dose?

Answer 16

Absorbed dose is the energy deposited per unit mass of material.

1 Gray (1 Gy) = 1 Joule of energy absorbed in 1 kg of material

Example: Typical radiation dose to kill bacteria (sterilisation) is 25 kGy.

Question 17

what is a dose equivalent?
what is it measured it

Answer 17

Dose equivalent takes into account the variation in biological effectiveness of different radiations. It is measured in sieverts (1 Sv).

Dose equivalent = Absorbed dose × Quality factor (for particular radiation)

For gamma and beta radiation the quality factor is 1, so 1 Sv = 1 Gy

For alpha radiation the quality factor is 20, so 20 Sv = 1 Gy

alpha is more damaging than gamma as 20sv compated to 1sv
as it hits a particle it gives off energy immediately
gamma does this in a longer period of space and larger volume.

Question 18

how can radiation be used diagnostically?

Answer 18

X-rays for diagnostics

Question 19

how can radiation be used therapuetically?

Answer 19

External beam radiation for therapeutics

Question 20

how can radiopharmaceuticals be used ?

Answer 20

Radiopharmaceuticals can also be used both therapeutically and diagnostically

Question 21

what is radiopharmacy?

Answer 21

Radiopharmacy – manufacture and use of radioactive medicines
PET scans for diagnostics
Radionuclide therapy for therapeutics

Question 22

what can you use therapeutically and diagnostically?

Answer 22

radiopharmacuetical and radiopharmacy?

Question 23

what is the therapeutic use of radiation and what should be considered?

Answer 23

Deliver therapeutic doses of ionising radiation to specific disease sites with high specificity
Therapeutic radiopharmaceuticals – radio-labelled molecules

Important points to consider:
Specific targeting
Clearance of radioactivity from non-target radiosensitive tissues
Decay properties of the radionuclide

Question 24

what is the mechanism of action of radiation?
(2 routes)

Answer 24

Radiation causes damage through two routes

1. Direct damage (minor component)
   DNA single (SSB) and double stranded breaks (DSB) (one double-stranded break per 25 single-stranded breaks)
2. Indirect damage (major component)
   Hydrolysis of water which then reacts with cellular components
   SSBs, DSBs, breakage of disulfide bridges in proteins

Question 25

what are the three approaches of radiotherapy?

Answer 25

Radiation used to treat cancer Three approaches: 1. External beam radiation 2.Sealed source radiotherapy – Brachytherapy 3. Unsealed source radiotherapy

Question 26

what is external beam radiation? when is higher and lower energy used?

Answer 26

Uses X-ray or gamma-ray radiation Higher energy than for diagnostic purposes Typical therapeutic energy 1-25 MeV (megaelectronvolts) Typical diagnostic energy 20-150 KeV (kiloelectronvolts) Lower energy range used to treat skin cancer Higher energy range used to treat internal tumours including bladder, bowel, prostrate, lung and brain

Question 27

what is sealed source radiotherapy (Brachytherapy)? what is it used for? what is the low dose rate and high dose rate?

Answer 27

Brachytherapy delivers radioisotopes sealed into capsules or wires Radiation can escape, but radioisotope cannot move from site of action Radioisotopes include iodine-125 or cesium-131. Effective treatment for cervical, prostate, breast, oesophageal and skin cancer low dose rate - up to 2Gy/h high dose rate - over 12 Gy/h

Question 28

what is low dose rate (LDR) branchytherapy (sealed) ? what is it used to treat? how long does it administer and exposure ?

Answer 28

Permanent implantation of radioactive seeds at site of action Low dose of radiation administered over weeks or months Typically use iodine-125 radionuclide (gamma-ray emission) Used to treat prostate cancer Low dose but long term exposure

Question 29

what is high dose rate ( HDR) barchytherapy - sealed?

Answer 29

Temporary insertion of radioactive wires into site of action. Can be combined with external beam radiotherapy. Commonly use iridium-192 (gamma-ray emission) High dose but short term exposure.

Question 30

what is the difference between HDR and LDR?

Answer 30

LDR: Low dose but long-term exposure over weeks or months HDR: high dose but short term temporary

Question 31

what is unsealed source radiotherapy?

Answer 31

Use of radiopharmaceutical to localise at specific targets Targeting due to properties of radiopharmaceutical (e.g. accumulation of iodine in thyroid) or administration route. Patient takes oral or IV solution of radiopharmaceutical Radionuclides used in UK include Iodine-131, Strontium-89 and Radium-223. α or β emission usually required

Question 32

what is the use of unsealed sources of radiotherapy?

Answer 32

More than 50% of patients with prostate, breast or lung cancer will develop painful bone metastases Pain relief can be achieved by treatment with 89Sr-strontium chloride (β-radiation source). When administered by the IV route, strontium is taken up by both the normal skeleton and, to a greater extent, skeletal metastases. Irradiation of the tumour deposits by the 89Sr induces pain relief.

Question 33

how can hyperthyroidism or thyroid cancer be treated?

Answer 33

Thyroid hormones are excessively released due to gland hyperfunction. The cells need iodine to make the hormone, so they absorb any iodine found in the body. 131I-sodium iodide is often prescribed to damage cells that make thyroid hormone. β-radiation source- reach site of action and penetrate - only to that organ not to the rest of the body. Administration of radiopharmaceutical: Oral, either as a solution or in a capsule Also used to treat thyroid cancer

Question 34

how are radiopharmaceutical used for diagnostic different than those for therapeutics

Answer 34

Radiopharmaceutical used for diagnostics are different than those for therapeutics Requires gamma emission, rather than α or β emission. Short half-life – a few hours Example: 99Tc – radionuclide with half-life 6 hrs and gamma emission.

Question 35

how are radiopharmaceuticals administered?

Answer 35

Radiopharmaceutical are administered via IV.

Question 36

how is radiopharmaceutical radiation detected?

Answer 36

The radiation is detected externally using a special scintillation detector, known as a gamma-camera.

Question 37

what is Positron emission tomography (PET) scan? how is it used to identify tumours?

Answer 37

Used to observe metabolic processes Imaging technique using radiolabelled glucose – fludeoxyglucose Contains 18F – a gamma source Localisation can be used to assess glucose metabolism Can be used to identify tumours due to an increased number of mitochondria in rapidly growing malignant masses

Question 38

what is renal isotope scan (MAG3 Renogram)

Answer 38

Used to test renal function Most common isotope - technetium Tc 99m mercaptoacetyltriglycine (99mTc-MAG3)

Question 39

what is technetium? when is it used?

Answer 39

Lightest chemical element with no stable isotope 99mTc – a metastable isotope of 99Tc Most commonly used radioisotope used in medicine Emits only gamma radiation Prepared in water from [99mTcO4]- Half life – 6 hours On-site preparation and injection into the patient

Question 40

what are examples of techetium?

Answer 40

The hexakis(alkyl isocyanide) complex of 99mTc(I) is an organometallic compound that has been successfully commercialised (Cardiolite)- Since Cardiolite treatment is non-invasive, it has become the most important myocardial imaging method.

Question 41

what are safety considerations of radiation?

Answer 41

Shielding Plastic and metals like aluminium can shield beta-rays. Lead and tungsten can shield gamma-rays. Distance The radiation dose is inversely proportional to the square of the distance Time - Minimizing the time spent handling a radioactive source will reduce a radiation dose